A control circuit for an inductive load

Claim 1

A unidirectional current (dc) control system for a switched reluctance machine having a stator defining stator poles, a rotor defining rotor poles and at least one phase winding, the system comprising: a rectifier, having an alternating current (ac) input and a dc output; a dc link capacitor; control means arranged to control the current supply to the phase winding from the capacitor; a voltage booster including an inductor arranged in the path of the current from the ac input; suppressor switch means arranged to control the supply of current to the dc link capacitor from the rectifier; sensing means for sensing deviation of the ac input current from a desired waveform and being operable to produce an output indicative of the deviation; and actuating means responsive to the deviation for actuating the voltage booster to compensate for the deviation to maintain the ac input current substantially following the desired waveform to suppress harmonics of the ac input current, and to charge the capacitor to a voltage in excess of a peak value at the ac input to the rectifier.

Claim 5

A system as claimed in any of claims 1 to 4 in which the actuating means include a modulator operable to produce an actuating signal for actuating the suppressor switch means in response to the said deviation.

Claim 7

A system as claimed in any of claims 1 to 6 in which the sensing means include a comparator arranged to receive a first input derived from the ac input current and a second desired waveform input indicative of the waveform of the ac input voltage.

Claim 8

A system as claimed in any of claims 1 to 7, including monitoring means for providing a capacitor signal indicative of the magnitude of the voltage across the dc link capacitor and means responsive to the capacitor signal for adjusting the amplitude of the desired waveform, thereby to maintain the dc link capacitor voltage at a predetermined level.

Claim 9

A method of suppressing harmonics in the control of an inductive load supplied from an alternating current (ac) supply using a unidirectional current control circuit comprising: first and second switch means, each switch means having first and second power terminals, the second power terminal of the first switch means being connected with one end of the load and the first power terminal of the second switch means being connected with the other end of the load; unipolarity capacitance means connected across the first power terminal of the first switch means and the second power terminal of the second switch means; first diode means connected to conduct from the first power terminal of the second switch means to the first power terminal of the first switch means; second diode means connected to conduct from the second power terminal of the second switch means to the second power terminal of the first switch means; and a rectifier arrangement having a unidirectional current output and including rectifier means, having ac input terminals and dc output terminals, and an energy storage inductor connected in series with one of the terminals of the rectifier means, the unidirectional current output of the rectifier arrangement being connected across the power terminals of the second switch means, the method comprising: a) rectifying the ac supply into a unidirectional supply; b) controlling the supply of current to the load from the capacitance means by actuating the first switch means; c) charging the capacitance means to a voltage in excess of the peak value of a voltage at the ac input terminals of the rectifier by actuating the second switch means; d) comparing the ac supply current waveform with a reference waveform; and e) controlling actuation of the second switch means to suppress the higher harmonic components of the current drawn at the ac input terminals.

Claim 12

A method as claimed in claims 9, 10 or 11, including controlling a supply of current to the load by actuating the first switch means substantially independently of actuation of the second switch means.